Method and material for obtaining photographic contrasts



Patented Jan. 12, 1937 ED STATES PATENT OFFICE METHOD AND MATERIAL FOROBTAINING PHOTOGRAPHIC CONTRASTS No Drawing. Application January 11,1935, Serial No. 1,436. in Germany February 5, 1934 15 Claims.

This invention relates to a method and mate-' rial -for obtainingphotographic contrasts with the aid of light.

It is known to obtain photographic contrasts by exposing a carrier whichhas been sensitized by a diazonium compound, and using metal salts toobtain permanent colored pictures in various tones. For instance, it hasbeen proposed to produce photographic contrasts by means of a sensitizedlayer containing a mixture of a diazonium compound and a silver salt,which layer upon exposure gives a silver picture. The layer is thentreated with an alkaline liquid and subsequently with a fixing agent.

The object of the present invention is to produce with diazoniumcompounds pictures of better contrast effects than the above mentioned.

According to our invention pictures are produced photochemically byusing a diazonium compound and a mercurous salt. Preferably themercurous salt is embedded in the layer provided with the diazoniumcompound, although good results can be obtained by using the mercuroussalt only after the exposure of the layer contain- 25 ing the diazoniumcompound. While we believe that. the picture formation is due to theformation of metallic mercury resulting from the reduction of themercurous salt by the light decomposition product of the diazoniumcompound,

0 we do not wish to commit ourselves to this explanation.

The fixation of the pictures obtained according to the invention can beefiected in a simple manner by rinsing with water. In contradis- 35tinction to the prior methods-in which silver nitrate has been used, andin which rinsing could 45 In order to increase the sharpness andcontrast effect of the picture, it is advantageous to place, subsequentto the exposure, the layer prepared according to the invention, in anenviron-'-- ment which is shut off from the light and which has a highcontent of water vapor, and to rinse it only after it has remained insuch environment for a time, in general for some hours.

The speed of picture formation of such a layer is dependent upon themoisture conditions of 5 the layer, including the amount of moistureprescut at the time of the exposure. The greater the moisture present atthe time of exposure the greater is the visibility of the picturedirectly after the exposure. If a layer contains very little moisture atthe time of the exposure, and after exposure is kept in a very dryenvironment, which is shut oil? from light, substantially no pictureformation will take place. However, if the layer, at the time of'theexposure, has the degree of moisture generally obtained by drying in theair, some visible picture formation often occurs immediately after theexposure. degreepfdryness during the exposure other than air-dry isnotpreferred. The speed of the picture formation after the exposure can begreatly increased both by a high degree of humidity and by heating,which may be effected by treatment in a. hot water bath or with hotwater vapor or steam.

As a rule the resulting color of the picture depends upon the time ofexposure and also upon the quantity of the mercurous salt used.

' We have found that the useful properties of the sensitized materialsaccording to the invention are offset to some extent by the disadvantagethat with-many carrier materials, for instance paper and linen, thepicture produced in accordance with the invention fades out after sometime. This is probably due to the subsequent formation by oxidation,first of mercurous compounds and finally of mercuric compounds.

We have found, however, that this fading out may be efiectivelyprevented by using, in combination with the mercurous salt, the salt ofa second metal, which lies higher in the potential series of metals thandoes mercury, as for instance, silver, gold or platinum.

The combined application of the two metal salts can be carried out invarious manner, for instance by treating the picture produced withdiaz'onium compound and mercurous salt in accordance with the invention,with a silver nitrate solution, and by subsequently bathing it in asolution of sodium sulphite to remove the excess silver nitrate, as wellas any mercury nitrate which may be formed. I

It is also possible to subject the picture pmduced according to theinvention, to a short treatment with a silver nitrate solution, andsubsequently to a short duration rinsing with distilled water, and todevelop the picture with a solution of metol citric acid or of metoltartaric acid. This may be efiected immediately after the exposure. forinstance, at a time when the picture is still completely invisible.

A particular Even for pictures, the layer of which consists only ofdiazonium compound and of a mercurous salt-thus without the use of asecond metal salt-a washing with a weak acid solution, for

However, even when using the weak acid'treatment, the pictures tend toultimately fade out, which is not the case when, in addition to a mer- 1curous salt, a second metal salt is used, as state above.

Irrespective of whether only a mercurous salt is used, or both amercurous salt and a second metal 'salt, the initial sharpness and thecontrast eifect of the picture are much greater than when using only asilver salt. Thus the initial sharpness and contrast effect of thepicture are due to the presence of the mercurous salt, whereas thestabilization of the picture is obtained by the addition of the secondmetal salt. A further advantage of the images obtained in accordancewith the invention is their blackbrown color, which gives a much morepleasing appearance than the yellowish-brown tone pic- If pictures areto be treated in an aurichloride' tures obtained by means of diazoniumcompounds and silver salts only.

As stated, instead of using silver salts in combination with mercuroussalts, salts of other metals which are higher in the electric potentialseries of metals than is mercury, can be used for the stabilization ofthe image; for instance, the salts of gold can be used with goodresults, a suitable gold salt being, for instance, aurichloride.

solution it is, however, necessary to very carefully wash out thepicture after its exposure and tains besides the diazonium compound, amercurous salt and a silver salt. With such sensitized layers beautifuland very stable pictures can be obtained, the stability of thissensitized layer being materially increased for the purpose ofconserving it prior to its use.

Images having very high stability can also be obtained without usingsilver nitrate, by introducing the diazonium compound and the mercuroussalt into regenerated cellulose serving as carrier. Excellent resultscan be so obtained by using a carrier consisting of superficiallysaponified acetyl cellulose. The picture obtained with superficiallysaponified acetyl cellulose is particularly well adapted for use as atemplate or tracing from which prints can be made on socalled printingpaper. It has been found that in this manner positive images exhibitingphotographic half-tones can be excellently reproduced on the printingpaper.

.When the sensitized system according to the invention is provided on atransparent carrier, ior instance on the above-mentioned regeneratedcellulose, it is eminently adapted for use with socalled reflexphotography. By using transparent sensitized material obtained in theabove manner, very beautiful and sharp pictures are obtained. In thiscase the sensitized material is placed with its sensitized side on theoriginal to be reproduced and is exposed through the transparentsensitized material so that the light reflected by the original causespicture formation.

The invention will be more clearly understood by reference to thefollowing examples:

Example I Paper is soaked in a 2% solution of mercurous nitrate in waterand is then dried in the air.

Subsequently it is soaked in a 1% solution ofbenzene-diazonium-boron-fiuoride in alcohol, whereupon the so-treatedpaper is again dried in the air and exposed under a tracing for minutesto the light of a 5 kw. incandescent lamp placed at a distance of 25centimeters therefrom. The exposed paper, on which no picture isvisible, is washed in water for one hour and a grey negative picture isobtained. I

It is also possible to use diazonium compounds containing asubstitutent, for instance: l-diazoniumbenzenel-sulphonic acid.

Especially suitable are diazonium compounds containing a substitutentwhich consists of a 'hydroxyl group, for instance, in para-position, ofwhich we may mention the following:

1-hydroxybenzene-4-diazonium-boronfluoride,l-hydroxybenzene-4-diazoniuin-fiuosulphonate,1-hydroxybenzene-i-diazonium-2-sulphonic acid, l-hydroxybenzene 4diazonium 2 carboxylic acid, l-hydroxy-2-nitrobenzene-4 diazonium 6sulphonic acid.

Example II Paper is soaked in a solution ofl-hydroxy-benzene-i-potassium diazosulphonate and mercurous nitrate inthe ratio of 1 mol. potassium diazosulphonate to 2 mol. mecurous nitrateand then dried in the air. The sensitized material thus obtained isexposed under a tracing for 1 minute to the sunlight. After exposure anegative brown picture appears which, after being washed-in water forabout 20 hours, exhibits a grey-black tone and a sharp contrast.

It is also possible to use benzendiazonium compounds in which thesubstituent consisting of the hydroxyl group is present in themeta-position and of which the following examples are given:

l-hydroxybenzene 3 potassium diazosulphonate,

l hydroxybenzene-5 -diazonium 2 carboxylic acid,

l-hydroxybenzene-5-diazonium-4-sulphonic acidfi-carboxylic acid.

Still better results are achieved when the hydroxyl-group is present inthe ortho-position, with respect to the diazonium groups, for instance:

1-hydroxybenzene-2-potassium diazo sulphonate, l-hydroxybenzene 2.-diazonium fiuosulphonate.

Example III the air. When exposing the sci-sensitized paper under atracing for 2 minutes to the light of a kw. incandescent lamp, and at adistance of 25 centimeters therefrom, a picture is not yet visible. Onlyafter washing in water does a brown-grey negative picture appear.

Example IV Paper, provided with a gelatine layer. is soaked in a 1%solution of l-hydroxy-Z-diazoniumbenzene-l-sulphonic acid and a 2.5%aqueous solution of mercurous nitrate and is then dried in the air. Thesensitized paper is then exposed under a film negative for 1 minute tothe sunlight. The partly visible positive picture is developed in a 1%aqueous silver nitrate solution. The excess diazonium compound,mercurous salts and silver salts are removed, for instance, by washingwith water for one hour.

The print so obtained exhibits a brown-black tone and excellent sharpcontrast effects.

Example V positive picture exhibits a brown-grey tone. By

subsequently drying in the air, the color of the picture becomes darkerand acquires a blackbrown tone.

Upon rinsing with water at room temperature, the pictures appear inabout half an hour. By washing with hot water, for instance water at atemperature of. 50-60 C., the image is developed in 2 to 5 minutes. Forfixing it is desirable to again wash with water for a considerable time.By a treatment with 0.01 N. nitric acid or 0.1 N. acetic acid, thefixation can be effected in about one hour.

Example VI water. The picture thus produced is then converted into asilver picture in a 1% solution of silver nitrate.

The positive picture, which exhibits a deep brown tone, is fixed in asulphite solution and can then be advantageously used as a diapositivefor the printing process. If the mercury picture would not betransferred into'a silver picture in the silver nitrate solution, thedisadvantage is encountered that it will disappear in the course ofabout one year.

Example VII Regenerated cellulose is soaked in a 50% alcoform a 3/4%concentration and mercurous nitrate to form a 1.2% concentration, andthen dried in the air. The sensitized material thus obtained is exposedunder a glass negative for 2 minutes to the light of and at a distanceof 40 centimeters from a quartz mercury lamp; it is then exposed forhalf an hour to an atmosphere having a high content of water vapor andsubsequently washed in water, as a result of which a positive picture isdeveloped and rendered visible. Thereupon the picture is stabilized by atreatment with silver nitrate and subsequent rinsing with water.

Example VIII The acetyl cellulose, commercially known under theregistered trade-mark Sidacisol, is treated, for instance, in. a shakingmachine for two minutes with a 2 N. alcoholic potash lye solution, dueto which the acetyl cellulose is superficially saponifled. Afterthoroughly washing with water, it is dried between filtering paper andsubsequently soaked in a 2% mercurous nitrate solution. By means of arubber squeegeeths layer is squeegeed on a glass and again dried betweenfiltering paper. The material thus obtained is soaked in a 0.75%solution of l-hydroxy-2-diazonlum-G-methylbenzene-4-sulphonic acidcontaining 1.2% mercurous nitrate and 0.75% of silver nitrate.Thereupon, the sensitized material is conserved in the air for aconsiderable time, say for five days, in order to obtain a materialhaving the desired properties.

When exposing the sensitized material thus obtained under a photographicglass'negative for 2 to 3 minutes to the light of and at a distance of25 centimeters from a carbon arc lamp, a slightly visible positivepicture exhibiting a brown tone appears, which is then developed forminutes in a 1% silver nitrate solution having a temperature of 40 to 50C. Thereupon it is washed for about two hours with distilled water,followed by washing for about two hours with tap water and by a shorttreatment, for instance for about 1 minute, with a 1% sodium sulphitesolution and is again washed with water. After exposure it is alsopossible to develop with a solution containing 2% of metol-and 4% ofcitric acid; it being desirable, however, to reduce the time of exposureto about 1 minute, followed by washing for one minute with theabove-mentioned developer and by rinsing for half an hour with distilledwater. Finally it is washed for several hours with tap water and ifnecessary, after the said treatment with sodium sulphite. It isadvisable to finally treat with an approximately 20% solution ofglycerin in water in order that the sisting of a hydroxyl group,occupies the orthoposition relatively to the diazonium group, forinstance:

l-hydroxy-2-diazonium'benzene-4-su1phonic acid 7 B-carboxylic acid,

1 hydroxy 2 diazonium acid,

1 hydroxy 2 -diazonium benzene-4-chlorine-6- sulphonic acid,

l-hydroxy-G-acetylamino-Z-diazonium benzene- -sulphonic acid.

It is also possible to use diazonium compounds in which two hydroxylgroups are present in. the benzene nucleus, for instance1-hydroxy-2-diazobenzene-5-carboxylic nium-6-hydroxybenzene-4-sulphonicacid.

Instead of hydroxyl. it is also possible to substitute amino groups inthe benzene nucleus and one or both of the hydrogen atoms of such anamino group may be substituted in their turn.

Example IX Example X Paper is repeatedly, say three times, soaked in a2% solution of mercurous nitrate and subsequently bathed in a 6% sodiumsulphate solution and, in order to remove the formed sodium nitrate, itis rinsed with water for one hour. After the paper has been dried in theair, it is soaked in a 1% solution ofl-diazonium-Z-hydroxynaphthalene-4-sulphonic acid and it is then againdried in the air. This material may be used in the manner set forth inExample III. After being rinsed with water, the picture, which was notyet visible after the exposure, is developed to a grey negative print.

Example XI Paper is soaked in a 2% solution of mercurous nitrate and isthen dried in the air. Subsequently it is soaked in an 80% alcoholicsolution containing 1% of 2-hydroxy-l-diazoniumnaphthalenel-sulphonicacid and 1% of silver nitrate and is again dried in the air. Thesensitized material is exposed under a film negative for 30 seconds at adistance of 25 centimeters from a 5 kw. incandescent lamp and the notyet visible picture is developed by exposing the material for 24 hoursto an atmosphere having a high content of water vapor. In this case thetone of the picture at first becomes brown and later becomes black. Inorder to fix the picture it is washed with water; the color of thepicture not being changed.

Example XII Instead of incorporating the materials referred to inExample XI in paper, they may also be incorporated ina carrierconsisting of superficially saponified acetyl cellulose. For preparingthe light sensitive material and for producing pictures thereon, one mayproceed in accordance with Example VIII.

Example XIII Paper is smeared with a 2% solution of mercurous nitrate, a1% solution of 1-diazonium-2- hydroxynaphthalene-i-sulphonic acid, and a2% solution of mercurous nitrate. After each operation the treated paperis dried in the air. Subsequently it is exposed under a tracing for ashort time (for 30 seconds at a distance of 25 centime- 5 ters from a 5kw. incandescent lamp) and developed for 5 minutes in a 1% solution ofaurichloride. A negative violet-red picture appears which is stabilizedby rinsing with water.

- Since mercurous nitrate reacts with aurichloride, it is advisable todevelop after the exposure and to then rinse out thoroughly with water;the picture thus obtained being finally treated with the aurichloridesolution.

Example XIV Paper is smeared with a 1% solution ofl-diazonium-2-hydroxynaphthalene-4-sulphonic acid and dried in the air.After being exposed under a tracing for a short time (for 30 seconds ata distance of 25 centimeters from a 5 kw. incandescent lamp), thetreated paper is smeared with a 2% solution of mercurous nitrate inwater. Thus the picture is developed in about 5 minutes whereupon it iswashed with water and after 25 that treated with a silver nitratesolution.

It is also possible to rub a veryfine powder of mercurous nitrate intothe layer after the exposure, and to subsequently place the so-treatedlayer in a space having a high content of water 30 vapor. The pictureappears after about half an hour and can be stabilized in the manneralready set out above.

While we have described our invention in connection with specificexamples and in specific 35 applications we do not wish to be limitedthereto, but desire the appended claims to be construed as broadly aspermissible in view of the prior art.

What we claim is:

1. A method of producing photographic con- 40 bringing a mercurous saltinto reactive relation- 45 ship with the light-decomposition product ofthe diazonium compound in the presence of moisture to form thecontrasts.

2. A method of producing photographic contrasts comprising the steps,selectively exposing 50 a light-sensitive system containing a'diazoniumcompound to partly decompose the diazonium compound at selected portionsof the system, bringing a mercurous salt into reactive relationship withthe light-decomposition product of the 55 diazonium compound in thepresence of moisture to form contrasts, and applying to the system tostabilize the contrasts a salt of a metal lying higher than mercury inthe electric poten- 60 tial series of metals.

3. A method of producing photographic contrasts comprising the steps,selectively exposing a light-sensitive system containing a diazoniumcompound and a mercurous salt to partly decom pose the diazoniumcompound at selected por- 65 tions of the system, and moistening thesystem to form contrasts by the reaction between the mercurous salt andthe light-decomposition product of the diazonium compound.

4. A method of producing photographic contrasts comprising the steps,selectively exposing a light-senstitive system containing a diazoniumcompound to partly decompose the diazonium compound at selected portions.of the system;

adding a mercurous salt to the system, moistening the system to formcontrasts by the reaction between the mercurous salt .and thelight-decomposition product of the diazonium compound, and heating thesystem to increase the speed of contrast formation.

5. A method of producing photographic contrasts comprising the steps,impregnating a carrier of regenerated cellulose with a diazoniumcompound to form a light-sensitive sysem, selectively exposing saidsystem to partly decompose the diazonium compound at selected portions,and bringing a mercurous salt into reactive relationship with thelight-decomposition product of the diazonium compound in the presence ofmoisture to form the contrasts. I

6. A method of producing photographic contrasts comprising the steps,impregnating a carrier of regenerated cellulose with a diazoniumcompound and a mercurous salt to form a lightsensitive system therein,selectively exposing the so-iormed system to partly decompose thediazonium compound at selected portions thereof,

I and moistening the carrier to form contrasts by light-decompositionproduct of the diazonium compound in the presence of moisture to producethe contrasts.

8. A method of producing photographic contrasts comprising the steps,impregnating a carrier of superficially saponifled acetyl cellulose witha diazonium compound to form a lightsensitive system, exposing saidsystem by reflex I photography to partly decompose the diazoniumcompound at selected portions, and bringing a mercurous salt intoreactive relationship with the light-decomposition product 01 thediazonium compound in the presence of moisture to form the contrasts.

9. A material for obtaining photographic contrasts comprising a carrier,and a light-sensitive system supported by said carrier and comprising adiazonium compound and a mercurous salt.

10. A material for obtaining photographic contrasts comprising acarrier, and a light-sensitive system supported by said carrier andcomprising a diazonium compound, a mercurous salt, and a stabilizerconsisting of a salt of a metal lying higher than mercury in theelectric potential series of metals.

11. A material for obtaining photographic contrasts comprising a carrierof regenerated cellulose, and a light-sensitive system within saidcarrier and comprising a diazonium compound,

and a mercurous salt.

- contrasts comprising a suitable carrier, and a light-sensitive systemsupported by said carrier and comprising a diazonium compound andmercurous boronfiuoride.

15. A material for obtaining photographic contrasts comprising asuitable carrier, and a light-sensitive system supported by said carrierand comprising a diazonium compound and mercurous sulphate.

ROELOF JAN HENDRIK ALmK. KLAAS HINDERIKUS KLAASSENS. HARKE JAN HOUTMAN.

